LC/MS is known as a complementary analytical technique that combines high-performance liquid chromatography (HPLC) as a tool for quantitative separation analysis and mass spectrometry (MS) as a definitive tool for material identification, and is used for analysis of structures and functions of biomolecules, and the like.
Particularly, nano-LC/MS optimized to perform ultramicroanalysis of biological components is widely used as one of the powerful tools for protein identification in the field of post-genome research. Nano-electrospray ionization (nano-ESI) is a technique for online coupling of nano-LC to MS, and uses an emitter formed from a capillary having a sharp tip such as an emitter 42 as shown in FIG. 10.
Nano-electrospray ionization is performed by allowing a solution containing an analyte to pass through an emitter at a flow rate of about 10 nL/min to 1 μL/min and applying a high electric field across the distal end of the emitter and a sample inlet of a mass spectrometer. In this case, the sample solution can be sprayed without using an atomizing gas to ionize the analyte.
Nano-LC generally uses a nano-column having a small column volume and an inner diameter of 75 μm to treat a trace amount of sample solution. In the case of nano-LC, extra-column dead volume causes serious deterioration in separation capacity, and therefore a dead volume created at a junction between an emitter and a column should be minimized. As a result, the diameters of capillaries for use as emitters have already been reduced to several tens of micrometers, and the diameters of distal ends of emitters have already been reduced to several micrometers to efficiently ionize a sample eluted from nano-LC and introduce the ionized sample into a mass spectrometer.
Patent Document 1: Japanese Patent No. 3317749
Patent Document 2: Japanese Patent No. 3397255
Non-Patent Document 1: Anal. Chem. Vol. 78, No. 16, pp. 5729-5735 (2006)